The world is full of conundrums. Every second, the sun emits enough energy to meet all of humanity’s power needs for more than two hours. And yet, in 2019, only about 2% of global electricity came from solar. Hard costs for solar panels have more than halved since 2000; soft costs have fallen too – so what gives? Certainly not a lack of activity or will within academia, that much is clear. As the race towards a net zero energy future marches on, researchers are hard at work developing innovations that will help us to more efficiently capture and utilise the sun’s rays.
In the UK, one such hub of innovation is the University of Exeter, where experts work on everything from solar-powered textiles to heat pump design. The university as a whole sets the climate emergency and sustainability high on its list of priorities: last year it took home the Guardian University Awards Sustainability award for its work on setting up a climate emergency working group.
Prof Tapas Mallick leads the solar energy research group and is involved in two projects with particularly practical applications. The first is building-integrated photovoltaics for construction materials – or simply, solar bricks. Essentially, they are what it says on the tin: glass bricks strong enough to be used as a construction material, fitted with a mini solar panel inside. Mallick explains that an optical device embedded within magnifies the light so, even though the “brick” is small, it’s still very efficient at capturing light and converting it into electricity.
“[Another] benefit is that you don’t see them from the outside,” he says. To the untrained eye, buildings built with solar walls would look like any other tastefully designed glass building. What’s more, the bricks could cover a greater area than typical solar panels – the entire height of a skyscraper, for instance, rather than just the roof. So even though electricity generation is lower than with large panels, a net gain in power production is possible.
The bricks can also adjust levels of brightness inside the building, via the optical device. So if it’s a very sunny day, light can be minimised to a more suitable level for indoors. As can temperature. The bricks effectively adjust for the greenhouse effect that often occurs with glass, helping to keep the indoor temperature in a comfortable range. “Your heating or cooling load in the building is minimised,” says Mallick.
And the benefits keep on coming: there is also potential for these energy-harvesting bricks to be integrated into outdoor structures such as railway platforms or bus shelters. Mallick and fellow researcher Dr Hasan Baig, along with commercialisation manager Jim Williams, have put together a consortium of interested parties including Arup, Network Rail and HS2, with the aim of commercialising their innovation.
Glazing a trail
Smart glazing technology is another area where Mallick and his team are leading the way towards more energy efficient buildings. They have developed a type of window glazing that reduces heat loss in winter and can control incoming solar radiation in summer. “It will not only reduce the amount of heat going into the building envelope, it will absorb the heat and store it in thermal form, to be used later in the evening when needed,” he says.
In theory, a building which combines these two innovations – solar bricks and smart glazing – isn’t inconceivable. And Mallick says his team is working on such a concept, whereby buildings would give energy back to the grid rather than consuming it. “We are calling them energy positive buildings.”
Solving a bottleneck with a funnel
If capturing and utilising solar energy in novel and efficient ways is the name of the game, Mallick is not alone in this quest. Professor of nanoscience and nanotechnology Monica Craciun and professor of quantum systems and nanomaterials Saverio Russo are also leaders in this field. They have developed a technique for improving the efficiency of solar panels through what’s known as “funnelling”.
Conventional silicon solar panels typically have about 20% efficiency – that is, only 20% of the energy that reaches it is actually converted into electricity. Even pioneering new models, such as those made of perovskite crystal, reach only about 27% efficiency. According to Russo and Craciun, the funnelling technique could increase efficiencies by up to 60%.
Russo explains that when light hits the large surface area of the panel, the resulting charges that are created need to travel across the panel so they can be siphoned off and used as electricity. Usually, an external battery is used to store the charge within the panel. But this process is not very efficient because a portion of the energy harvested is used to move the charges into the battery. “The process … is a bottleneck that imposes severe limitations on the efficiency of this energy harvested from the sun,” he says. “So the idea was, let’s engineer this structure such that we have an effective slope of the terrain of the electrodes inside the solar panel, that efficiently and naturally moves them towards the battery without the need of any external intervention,” he says. Essentially, a funnel.
To do this, they work with nanomaterials – such as graphene, which is no more than one atom thick. And this was where Craciun and her team came in. “We basically had to engineer semiconductors and dielectric materials to create these gradients. So [I worked on the] engineering of these properties,” she says. Using nanoscale materials has implications not just for the efficiency of panels but also their size. In future, solar funnelling could mean that one panel the size of a small book easily powers an entire household, says Saverio.
Since publication of their breakthrough paper in 2018, work has continued on the advancement and potential commercialisation of this technology; a consortium of interested parties has been formed, with a view to scaling it up.
And as for when we might begin to see solar bricks, smart glazing and book-size panels on our homes and businesses, it’s difficult to say. But real action is afoot so there’s reason to believe that, given time, these technologies will see the light of day.
The Future of Energy
The University of Exeter are leaders in the Future of Energy. Take a look at courses available to study with them in this field: greenfutures.exeter.ac.uk/courses